Some 2-amino-4,6-diarylpyrimidines (APM), synthesized from chalcones and guanidine hydrochloride in presence of alkali by microwave irradiation in solvent-free conditions, were subjected to oxidation with chromium(VI)–oxalic acid complex (Cr(VI)–Oxa) in highly acidic solutions. Oxalic acid (Oxa) offers the reaction a more favourable pathway and in the absence of oxalic acid the reaction is sluggish. The depletion of chromium(VI) shows a complicated kinetics involving a fast reaction to about 35% consumption followed by a slow one. Low dielectric constant of the medium facilitates the reaction. The investigations with 2-amino-6-(4-nitrophenyl)- 4-phenylpyrimidine and 2-amino-6-(4-methoxyphenyl)-4-phenylpyrimidine reveal that, irrespective of the nature of the substituents, the rates are higher than for the parent. APM is catalytically converted to the unusual product 3-hydroxy-1,3-diphenyl-propan-1-one. Consideration of the kinetic behaviours under different experimental conditions and the product assignment provide valuable mechanistic insight into the system studied.